Shift-by-wire transmission

ABSTRACT

A shift-by-wire transmission system is provided. The system includes a gearbox that is configured and arranged to receive a rotational input and provide a select rotational output. The gearbox includes a plurality of gear assemblies that are operationally coupled together to provide the select rotational output from the rotational input. A shift assembly is operationally coupled to the plurality of gear assemblies of the gearbox to selectively change gearing of gearbox. An electric motor is operationally coupled to the shift assembly to activate the shift assembly to selectively change the gearing of the gearbox. A manual shift override is employed that is coupled between the shift assembly and the electric motor. The manual shift override is configured and arranged to manually disconnect the electric motor from the shift assembly and activate the shift assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/281,649, entitled “SHIFT-BY-WIRE TRANSMISSION”, filed on May 19,2014, which claims the benefit and priority to U.S. ProvisionalApplication Ser. No. 61/825,257, entitled “SHIFT-BY-WIRE CVT”, filed onMay 20, 2013, which is incorporated in its entirety herein by reference.

BACKGROUND

Traditionally the changing of gears in a gearbox of a vehicle is done bymechanical linkage. Shift-by-wire systems have been developed in whichtransmission modes are engaged/changed in an automobile without anymechanical linkage. However, current shift-by-wire designs do not lendthemselves well to all-terrain/utility task vehicles (ATV/UTV) and thelike. These types of vehicles are subject to harsh conditions and areused in remote locations. If a shift-by-wire transmission fails in gearat a remote location, the design in current shift-by-wire transmissionsor transfer cases used in the auto industry would need to be torn apartto disengage or place the transmission into neutral before the vehiclecould be moved.

For the reasons stated above and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art fora shift-by-wire transmission that lends itself to ATV/UTV vehicles.

SUMMARY OF INVENTION

The above-mentioned problems of current systems are addressed byembodiments of the present invention and will be understood by readingand studying the following specification. The following summary is madeby way of example and not by way of limitation. It is merely provided toaid the reader in understanding some of the aspects of the invention.

In one embodiment, a shift-by-wire transmission system is provided. Theshift-by-wire transmission includes a gearbox, a shift assembly, anelectric motor and a manual shift override member. The gearbox isconfigured and arranged to receive a rotational input and provide aselect rotational output. The gearbox includes a plurality of gearassemblies that are operationally coupled together to provide the selectrotational output from the rotational input. The shift assembly isoperationally coupled to the plurality of gear assemblies of the gearboxto selectively change gearing of gearbox. The electric motor isoperationally coupled to the shift assembly to activate the shiftassembly to selectively change the gearing of the gearbox. The manualshift override member is coupled between the shift assembly and theelectric motor. The manual shift override member is configured andarranged to manually disconnect the electric motor from the shiftassembly and activate the shift assembly.

In another embodiment, another shift-by-wire transmission system isprovided. The shift-by-wire transmission system includes a gearbox, ashift drum, an electric motor and spring loaded shift cam. The gearboxis configured and arranged to receive a rotational input and provide atleast one select rotational output. The gearbox includes a plurality ofgear assemblies operationally coupled together to provide the at leastone select rotational output from the rotational input. The shift drumassembly is operationally coupled to the plurality of gear assemblies toselectively change gearing of the gearbox. The electric motor isoperationally coupled to the shift drum assembly to activate the shiftdrum assembly to selectively change the gearing of the gearbox. Thespring loaded shift cam is operationally coupled to the shift drumassembly and is configured and arranged to complete a shift into aselect gear without the aid of the electric motor.

In further yet another embodiment, another shift-by-wire transmissionsystem is provided. The shift-by-wire transmission system includes agearbox, a shift drum, an electric motor, a spring loaded shift cam anda manual shift override member. The gearbox is configured and arrangedto receive a rotational input and provide at least one select rotationaloutput. The gearbox includes a plurality of gear assemblies that areoperationally coupled together to provide the at least one selectrotational output from the rotational input. The shift drum assembly isoperationally coupled to the plurality of gear assemblies to selectivelychange gearing of the gearbox. The electric motor is operationallycoupled to the shift drum assembly to activate the shift assembly toselectively change the gearing in the plurality of gear assemblies. Thespring loaded shift cam is operationally coupled to the shift drumassembly and is configured and arranged to complete a shift without theaid of the electric motor. The manual shift override member is coupledbetween the shift drum assembly and electric motor. The manual shiftoverride member is configured and arranged to manually disconnect theelectric motor from the shift drum assembly and activate the shift drumassembly without disassembling the gearbox.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more easily understood and furtheradvantages and uses thereof will be more readily apparent, whenconsidered in view of the detailed description and the following figuresin which:

FIG. 1 is a side perspective view of a continuous variable transmission(CVT) system of one embodiment of the present application;

FIG. 2 is a first side perspective view of a gearbox of the CVT systemof FIG. 1;

FIG. 3 is a second side perspective view of the gearbox of FIG. 2;

FIG. 4A is a partial first side perspective view of the gearbox of FIG.2 unassembled;

FIG. 4B is a partial second side view of the unassembled gearboxillustrating the remaining elements to FIG. 4A;

FIG. 5A is a first side perspective view of the shift-by-wire componentsof the gearbox of an embodiment of the present invention;

FIG. 5B is a second side view of the shift-by-wire components of FIG.5A;

FIG. 5C is a partial cross-sectional side view of the shift-by-wirecomponents illustrated in FIG. 5A;

FIG. 6 is side perspective view with a partial cross-sectional view of agear train of shift-by-wire components of one embodiment of the presentinvention;

FIG. 7 is an unassembled side view of a shift drum assembly of oneembodiment of the present invention;

FIG. 8A is a side view of the shift-by-wire components illustrating dogclutch teeth of a park dog clutch meshing with park plate teeth of apark plate of an embodiment of the present invention;

FIG. 8B is a side view of the shift-by-wire components illustrating dogclutch teeth of a park dog clutch not meshing with park plate teeth of apark plate of an embodiment of the present invention;

FIG. 9A illustrates a side perspective view of the shift drum assemblyillustrating the interaction of a shift cam and shift drum housing witha shift fork positioning pin in a first position within a track;

FIG. 9B illustrates a side perspective view of the shift drum assemblyillustrating the interaction of the shift cam and shift drum housingwith the shift fork positioning pin in a second position within thetrack;

FIG. 9C illustrates a side perspective view of the shift drum assemblyillustrating the interaction of the shift cam and shift drum housingwith the shift fork positioning pin in a third position within a track;

FIG. 10 is a side perspective view of a shifting assembly of anotherembodiment;

FIG. 11 is a rear perspective view of the shifting assembly of FIG. 10;

FIG. 12 is a block diagram of a shift control system of one embodimentof the present invention;

FIG. 13A is a target window pie chart of one embodiment of the presentinvention:

FIG. 13B is a drum cam track graph of one embodiment of the presentinvention;

FIG. 14 is an operational flow diagram of one embodiment of the presentinvention; and

FIGS. 15A through 15E are target window pie charts illustrating theshifting operations of one embodiment of the present invention.

In accordance with common practice, the various described features arenot drawn to scale but are drawn to emphasize specific features relevantto the present invention. Reference characters denote like elementsthroughout Figures and text.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the inventions maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that changesmay be made without departing from the spirit and scope of the presentinvention. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present invention isdefined only by the claims and equivalents thereof.

Embodiments of the present invention provide a gearbox that shifts gearranges via an electric shift motor that is controlled by an electricsignal from an operator input device rather than a mechanical linkage.In embodiments, a manual-mechanical override is provided in case ofelectrical power failure or failure of the electric shift motor.Moreover, in embodiments, a spring loaded cam mechanism is provided forpark gear. Embodiments also provide a hybrid transmission system thatcontrols both gear ranges (high/low) as well as direction(forward/reverse). This hybrid configuration makes split control ofrange and direction possible. Embodiments also provide an auto shift topark at a vehicle power down. In addition, some embodiments provide amotor control algorithm that acts as an electronic detent to maintainproper position while at the same time preventing unwanted motorstarts/stops.

Referring to FIG. 1 a first side perspective view of a continuousvariable transmission (CVT) system 50 that implements a shift-by-wireembodiment of the present application is shown. The example CVT system50 includes a primary clutch 600 that would be coupled to the crankshaftof a motor (not shown), a second clutch 630 that is coupled to an inputshaft 272 of a shift-by-wire gearbox assembly 100 (gearbox 100) and abelt 620 that transfers rotation of the primary clutch 600 to thesecondary clutch 630. As known in the art, each of the primary andsecondary clutches 600 and 630 have movable sheaves that selectivelyposition the belt 620 select distances from respective center posts toset a then current gear. FIG. 2 illustrates a first side perspectiveview of the gearbox 100 without the primary and secondary clutches 600and 630. The gearbox 100 includes a first housing section 102 and asecond housing section 104. Also illustrated in FIG. 2 is the inputshaft 272 in which the secondary clutch 630 is coupled to provide inputrotation. Also illustrated is a front output shaft 122 with spines 122 aupon which an assembly is coupled to provide a rotational force to thefront wheels of a typical four wheel drive vehicle (not shown). FIG. 2further illustrates splined bore 182 a. The splined bore 182 a is usedto convey rotation to rear wheels of the vehicle (not shown). FIG. 3illustrates a second side perspective view of the gearbox 100.Illustrated in this view is manual shift override activation head 420 awhich is selectively rotated to override an electronic shift-by wireconfiguration. This is further discussed below in detail.

An unassembled view of the gearbox 100 of one embodiment is illustratedin FIGS. 4A and 4B. As discussed above, the gearbox 100 includes a firsthousing section 102 and a second housing section 104 that make up thehousing of the gearbox 100. The first housing section 102 is coupled tothe second housing section 104 via fasteners 106. Aligning pins 509 areused to align the first housing section 102 to the second housingsection 104 during attachment. The gearbox 100 includes a plurality ofgearing assemblies that are housed within the housing. In particular,the gearing assemblies include a front output assembly 120, a secondshaft assembly 200, a third shaft assembly 150, a fourth shaft assembly160, a rear output assembly 180, a shift fork assembly 240, an inputassembly 270 and a shift assembly 300. The shift assembly 300 in thisembodiment is a shift drum assembly 300. The housing sections 102 and104 are designed to hold the gearing assemblies in select locations inrelation to each other. For example, housing 104 includes receiving tube557 to receive the front output assembly 120. Housing 104 also includesa first gear aperture 530 that extends into the receiving tube 557. Ashaft 162 of the fourth shaft assembly 160 is received within the firstgear aperture 530 and is in operational communication with the outputassembly 120. Housing 104 also includes an idler seat 532 to hold a ballbearing 159 of the third shaft assembly 150. Housing 104 furtherincludes a main seat 534 to hold a ball bearing 239 of the second shaftassembly 200. Housing 104 includes an input aperture 536. An input shaft272 of the input assembly 270 extends through the input aperture 536. Aseal 524 is received within the input aperture 536. Housing 104 alsoincludes a rear output assembly aperture 522. Bearing 186 of the rearoutput assembly 180 and seal 512 are received in the rear outputassembly aperture 522. Housing section 104 also includes a shift forkseat 537 to hold an end of the shift fork assembly 240 and a shift drumseat 538 to hold an end of the shift drum assembly 300. The firsthousing 102 has similar features to hold the gearing assemblies inposition so they can operationally communicate with each other. Forexample, the first housing assembly 102 also includes a rear outputassembly aperture 520 to receive a bearing 184 of the rear outputassembly 180 and a seal 510.

The output assembly 120 includes, a front output shaft 122 upon which abearing carrier 124, gear 137, ball bearings 126, 138, washer 139,retaining rings 134, 140, shims 128 and 132, retaining ring 130 and lipseal 136 are mounted. The third shaft assembly 150 includes a thirdshaft 151 upon which a gear 152, washer 156, retaining ring 158 and ballbearings 154 and 159 are mounted. The fourth shaft assembly 160 includesfourth shaft 162 upon which is mounted ball bearings 166 and 176,retaining ring 174, gear 170 and washer 172. Also included with thefourth shaft assembly 160 is a bearing cover 168 that is received on thefourth shaft 162 and is designed to be attached to an inside surface ofthe second housing section 104 via fasteners 178 to cover bearing 166.Bearing 166 is received in a bearing seat 531 around the first gearaperture 530 in the inside surface of the housing section 104. The rearoutput assembly 180 includes gear 182. Bearings 184 and 186 are mountedon opposite sides of a center post of gear 182. Bearings 184 and 186 arereceived in seats around the second gear assembly aperture 522 andsecond gear assembly aperture 520 of the respective housing sections 102and 104. The second shaft assembly 200 includes a second shaft 202 uponwhich is mounted a low gear 204, needle bearings 206, 220 and 232,washers 208, 222, 230 and 236, retaining rings 210, 224, 228 and 238,park shift dog 212, ball bearings 214 and 239, sprocket 216 with chain218, engagement dog 226 and gear 234. The shift fork assembly 240includes shift fork rail 242 upon which is mounted a pair of shift forks250 and 256 that engage the respective park shift dog 212 and engagementdog 226 of the second shaft assembly 200. Also mounted on the shift forkrail 242 are retaining rings 246 and 262, cup washers 244 and 260,compression springs 248, 252, 253, and 258, and shift collar 254. Theinput assembly 270 of this embodiment includes an input shaft 272 uponwhich bearings 274 and 276, and sleeve collar 278 are mounted. The shiftdrum assembly 300 includes a shift drum 302. The shift drum 302 includesa shift drum housing 301 with a shift drum post 301 a upon which aspring loaded shift cam 320 with shift cam spring 322, retaining ring326 and a washer 324 are mounted. The shift drum assembly 300 in thisembodiment includes an angular position sensor to determine the angularposition of the shift drum 302 (setting of the shift drum 302).Moreover, in this example embodiment, a Hall effect position sensorassembly is used. In particular, mounted to an end of the shift drum isa non-ferrous bushing 328 that holds a magnet 330. A Hall effect rotaryposition sensor 511 a, as illustrated in FIG. 4A, is mounted proximatethe magnet 330. The Hall effect rotary position sensor is mounted inthis embodiment via fasteners 513. Sensor wires 511 are coupled to acontroller, discussed below, to monitor the angular orientation of shiftdrum housing 301 (i.e. the setting of the shift assembly). Although, aHall effect position sensor is shown, other types of position sensorsknown in art can be used. Moreover, although the magnet 330 in the Halleffect type system described above is mounted on the bushing 328, otherconfigurations such as, but not limited to, integrating the magnetinternally within the shift drum housing 301, mounting the magnet on theshift drum housing 301, and implementing the magnet in a rotorconfiguration such that as the drum housing 301 rotates the rotorrotates are contemplated. A detailed discussion of the shift drumassembly is provided below.

Referring to FIG. 4A, a first rear mount bracket 106 is mounted on thefirst housing section 102 and a second rear mount bracket 108 is mountedon the second housing section 104 via fasteners 110. The gearbox 100includes a speed sensor 112 that is operationally coupled to monitor theassemblies of the gearbox to determine a speed. The speed sensor 112 iscoupled to the first housing section in this embodiment via o-ring 113and fastener 119 configuration. A vent tube 121 is used to vent thehousing. The first housing section 102 further includes an outer cavity103 that houses a gear train 431 discussed below. A first motor cover114 is designed to cover the outer cavity 103 via fasteners 115. Analignment pin 123 is used to align the first motor cover 114 in relationto the first housing section 102 to cover the outer cavity 103. Thefirst motor cover 114 includes a motor cavity 111 in which an electricmotor 400 is received. A wire harness bracket 109 is coupled to thefirst motor cover 114. A second motor cover 116 is then coupled to covermotor cavity 111 via fasteners 117. A manual shift override member 420passes through apertures in the second motor cover 116, the first motorcover 114 and the first housing section 102 to engage the shift drumassembly 300. The manual shift override member 420 includes amanipulation head portion 420 a that is configured to be manipulated tooverride an electric shifting mechanism as further discussed below indetail. The manual shift override member 420 further includes externalsplines 420 b proximate a second end and a release section 420 c that isproximate the external splines 420 b. The release section 420 c of themanual shift override member 420 has a diameter that is less than thediameter of the external splines 420 b section. Further mounted on themanual shift override member 420 are washers 430, retaining ring 432,override biasing member 434 and an decoupleable shift gear 436.Positioned within the outer cavity 103 is a first gear train shaft 438upon which a seal 440, bearings 444 and a first gear 442 and a secondgear 446 are mounted. The first gear train shaft 438 is coupled to themotor 400. Also positioned within the outer cavity 103 is a second geartrain shaft 450 upon which is mounted a third gear 452, a fourth gear454 and respective bearings 456. Also shown in FIG. 4A is plug 502 thatthreadably blocks an output port (not shown) in the first housingsection 102 and plug 504 that threadably blocks an output port 503 inthe second housing section 104. Moreover, a park plate 506 is coupled tothe first housing section 102 via fasteners 507.

FIGS. 5A and 5B illustrate first and second side perspective views ofthe shift-by-wire components of the gearbox 100 without the housing. Thecomponents include the shift drum assembly 300, the shift motor 400, themanual shift override member 420, the shift fork assembly 240 and thesecond shaft assembly 200. The FIGS. 5A and 5B illustrates how theassemblies are in working communication with each other. The shift drumassembly 300 includes a shift drum 302 with a housing 301. An endsurface of the spring-loaded shift cam 320 and an end surface of thehousing 301 form a first shift fork groove 304 (or park shift forkgroove 304) in which a shift fork positioning pin 250 a of the firstshift fork 250 (or park shift fork 250) is received. The housing 301further has a shift collar groove 306 in which a shift collarpositioning portion 254 a of the shift collar 254 is received. The shiftdrum housing 301 further includes a second shift fork groove 308 inwhich a shift fork positioning pin 256 a of the second shift fork 256 isreceived. The shape of each of the grooves 304, 306 and 208 (orgenerally groove guides) are shaped to selectively move the respectivefirst shift fork 250, shift collar 254 and second shift fork 256 to adesired location to change the gearing of the gearbox 100 when the shiftdrum assembly 300 is rotated. That is, the shift forks 250 and 256 andrespective dog clutches 212 and 226 are moved by the shift drum 302. Ashift drum gear train 431 is used to rotate the shift drum 302. Theshift drum gear train 431 includes gears 442, 446, 454, 452 and 436 asdiscussed above. In normal operation, the motor 400 which is inoperational communication with the shift drum gear train 431 rotates theshift drum 302 to selectively move the shift forks 250 and 256 and theshift collar 254 of the second shaft assembly 200 to change gears of thegearbox 100. In embodiments, the manual shift override member 420 isconfigured to override the motor 400 when needed. In embodiments, thespring coupled mechanism described above is used not only for park gearsbut for all gears of the gearbox assembly 100.

FIG. 5C illustrates a cross-sectional view of FIG. 5A. Thiscross-sectional view illustrates that the shift drum housing 301includes interior splines 331 that engage the exterior splines 420 b onthe manual shift override member 420. This connection locks rotation ofthe manual shift override member 420 to the rotation of the shift drum302. Decoupleable shift gear 436 is selectively coupled to the manualshift override member 420 via the exterior splines 420 b. In particular,the decoupleable shift gear 436 includes interior gear splines 436 athat selectively engage the exterior gear splines 420 b on the manualshift override member 420. The biasing member 434 positioned betweenwasher 430/retaining ring 432 and the decoupleable shift gear 436 (bestshown in FIG. 5C) biases the decoupleable shift gear 436 to engage theexterior splines 420 b of the manual shift override member 420. As thepartial cross-sectional view of FIG. 6 illustrates, the decoupleableshift gear 436 engages gear 451. Gear 451 is also part of the gear train431. Also illustrated in FIG. 6 is gear 455 positioned between gears 454and 452 on the second gear train shaft 450. Gear 446 rides on the firstgear train shaft 438 via bushing 444. Gear 442 is coupled to the firstgear train shaft 438. Gears 442 and 446 engage gears 454 and 455,respectively of the second gear train shaft 450. In one embodiment,gears 455 and 454 are cluster gears that are operationally coupledtogether. Similarly, 452 and 451 can be cluster gears operationallycoupled together. When the motor 400 is activated the gear train 431moves the decoupleable shift gear 436 that is coupled to the manualshift override member 420 that is in turn rotationally locked to theshift drum 302. If a manual override of shifting of the gearbox 100 isneeded, the manipulation head 420 a of the manual shift override member420 is pushed into the shift drum housing 301 countering the bias forceof bias member 434. This disengages the interior gear splines 436 a ofthe decoupleable shift gear 436 from the exterior gear splines 420 b ofthe manual shift override member 240 and positions the decoupleableshift gear 436 in the release section 420 c (best shown in FIG. 5C) ofthe manual shift override member 240. This disengages the gear train 431from the manual shift override member 420. The manual shift override 420can then be rotated to rotate the shift drum 302 to a desiredorientation to change the gearing of the gearbox 100.

Embodiments of the shift-by-wire system use a small low weight and lowcost electric motor that provides a quick shift cycle time. Moreover, arelatively high rpm motor with a large speed reduction gear ratio isused to achieve an appropriate rpm at the shift drum. A combination ofthe gear ratio, efficiency loss within the gear train and the torqueneeded to spin the motor's shaft 438, makes it difficult, if notimpossible, to backdrive the system from the shift drum mechanismwithout disconnecting the motor 400 from the shift drum 300 as describedabove. Hence, without the manual override system, if the vehicle loseselectrical power the operator will be stuck in whatever gear the gearbox100 was in at the time of the loss of electrical power. If the vehiclewas in “Park” the vehicle would not be able to be towed because thewheels would be locked by the gearbox 100. In a traditionalshift-by-wire system the transmission would have to be disassembled inorder to manually shift gears by rotating the shift cam system. Themanual override mechanism described above allows an operator todisengage the shift drum 302 from the electrical motor 400 andassociated gear train 431 to manually shift the gearbox 100.

Another advantage to the configuration of the assemblies 120, 150, 160,180, 200, 240 and 270 in the gearbox 100 is that it provides a gearbox100 that not only changes gear ratios it also changes both gear range(high/low) and direction (forward/reverse). Hence the gearbox 100provides a hybrid of a typical automotive driveline layout where forwardgear ratios and direction (forward/reverse) would be changed by thetransmission and gear range (High/Low and/or 2wd/4wd) would be changedby the transfer case. Gearbox assemblies typical of a CVT drivendriveline in ATV/UTV applications basically function as a transfer casefound in automotive car/truck application, but have to incorporate areverse gear that automotive does not have since they have separatetransmission to provide that function.

In embodiments, a park gear locks a gearbox shaft from rotating byoperatively connecting to the gearbox housing. This can be done with adog clutch riding on a shaft that locks to a meeting clutch plategrounded to the housing or via a pawl grounded to the housing thatengages the dog clutch on one of the shafts. Due to the nature of dogclutch shifting, there will be times when one shifts to park but theteeth do not line up, preventing the parts from dropping into full mesh.They will sit in a “blocked” or “top-to-top” condition. With purelymechanical shifting, one can utilize a spring-loaded detent to maintaina preload on the shifting mechanism such that as soon as the vehiclerolls a small amount and the teeth spaces lineup, the parts will finishthe shift and drop into full mesh. With an electric powered shiftmechanism, the motor 400 is trying to rotate the shift cam assembly 300to specific angular positions for each gear and then shut off. If thedog clutch 212 lands in the blocked condition while shifting into Parkwith an electric shift configuration, you cannot rely on a spring loadeddetent system to finish the shift because that would mean the detentwould need to be able to back drive the electric motor gear train oncethe parts lined up, which due to the ratio, efficiency and motor freewill torque, isn't always possible. To finish the shift, an electricmotor would need to stay energized to impart steady torque until thereis relative motion between the dog clutch teeth to achieve a fullymeshed engagement. This is undesirable because it will stall the motor,causing heat and waste electrical draw. Although, it is possible tooversize the motor and associated wiring to dissipate enough heat toprevent a stall, an undesirable cost and weight penalty will beincurred. One embodiment of the present invention utilizes aspring-loaded shift cam 320 that is a separate piece from the shift drum302 to address this problem. It allows (spring in\direct-couple out)functionality. If a park dog lands in a block condition, the shift motorcan rotate the shift drum to its target angular position and shut off.As a shift drum 302 rotates, a torsion spring 322 holds a torsionalpreload on the shift cam 320 such that shift cam tab 320 a is heldagainst surface 303 a with some preload force. As soon as the vehiclerolls slightly, allowing the dog clutches to engage, the shift camfinishes the shift. The direct-couple out feature of the shift cam 320allows the electric motor 400 to directly move the dog clutch out ofengagement without applying the work through a spring. For gearboxeswith a plurality of gear ranges, there is typically a limited amount ofrotation available at the shift cam mechanism (shift drum). For anelectric motor actuated shift drum, to keep the motor size, weight andcost down it is desired to get as much mechanical advantage in the shiftdrum cam tracks as possible. If you simply spring load the shift cam 320for both directions (going into and out of gear), one would have toallow for more angular rotation for the park gear position, which wouldhurt the goal of maximizing rotation versus mechanical advantage. If youshifted out of park and load conditions created friction that tries tohold the park dog clutches in mesh, the torsion spring would need tofirst wind up until the coil binds, at which point it would act like asolid connection that would then start to move the shift fork\dog clutchout of mesh. Once the shift is complete and the dog clutches are in fullengagement, they cannot pop out because the cam tracks blocks the forkfrom moving.

Referring to FIG. 7, an unassembled side perspective of the shift drumassembly 300 is illustrated. As discussed above and illustrated in FIG.7, the shift drum assembly 300 includes a shift drum 302 having a shiftdrum housing 301. The shift drum housing 301 includes a shift drum post301 a. The spring-loaded shift cam 320 is received around the shift drumpost 301 a. Formed within the shift drum post 301 a of the housing 301is a spring holding aperture 301 b. The shift drum housing 301 alsoincludes shift drum window 301 c that is positioned proximate the shiftdrum post 301 a. The shift cam 320 includes a shift cam tab 320 a whichis positioned within the shift drum window 301 c in the shift drumhousing 301 and a spring holding slot 320 b. The shift cam spring 322includes a first end 322 a which is received in the spring holding slot320 b of the shift cam 320 and a second end 322 b that is received inthe spring holding aperture 301 b in the shift drum post 301 a.

FIGS. 8A and 8B illustrates a side view of the shift drum assembly 300,the motor 400, the shift fork assembly 240 and the second shaft assembly200. FIG. 8A illustrates the dog clutch teeth 212 a of the park dogclutch 212 meshing with park plate teeth 506 a of the park plate 506.FIG. 8B illustrates the dog clutch teeth 212 a of the park dog clutch212 not meshing with park plate teeth 506 a of the park plate 506. Asdescribed above, the park plate 506 is grounded to the housing 102.FIGS. 9A-9B illustrate the position of the shift fork positioning pin250 a of the park shift fork 250 in track 304 of the shift drum assembly300 and the shift cam tab 320 a of the shift cam 320 in the window 301 cof the shift drum housing 301 when the dog clutch teeth 212 a of thepark dog clutch 212 is not meshed with park plate teeth 506 a of thepark plate 506. Referring to FIG. 9A, the park shift fork groove 304includes a first section 304 a that is generally perpendicular to anaxis of the shift drum housing 301, a second section 304 b (or rampsection 304 b) that extends generally at an angle from the first section304 a and a third section 304 c which is again generally perpendicularto the axis of the shift drum housing 301. The third section 304 cextends from the second section 304 b. When the teeth 506 a and 212 aare in a blocked position (not meshed when placed in park or anotherselect gear), the shift fork positioning pin 250 a of the park shiftfork 250 is in a blocked position that is illustrated in FIG. 9A. In theblocked position the shift fork positioning pin 250 a is not alignedwith the first section 304 a of the park shift fork groove 304. Torqueimparted on the shift cam 320 via the shift cam spring 322 causes theshift cam tab 320 a to be initially biased against the first side wall303 a of the window 301 c as also illustrated in FIG. 9A. As the shiftdrum housing 301 is rotated by either the torque applied from theelectric shift motor 400, or via torque from the manual shift override420, this torque counters the biasing torque supplied by the shift camspring 322 via the ramp section 304 b engaging the shift forkpositioning pin 250 b allowing the shift drum housing 301 to rotate inrelation to the shift cam 320. When this happens the shift cam tab 320 aof the shift cam 320 moves freely in the window 301 c of the shift drumhousing 301 toward the second side wall as illustrated FIG. 9B. Thisrelative motion creates additional torsion preload in shift cam spring322 and allows the shift drum 301 to reach its target angular position(park in this example) even though the shift cam 320 and shift forkpositioning pin 250 a have not. The shift system is now in a state ofpreload. If the vehicle rolls slightly, rotation at the wheel wouldcause relative motion between the park dog clutch 212 and the park plate506, which in turn allows the teeth 212 a and 506 a to engage. Forapplications other than Park gear, relative motion at the dog clutchescould come from rotation of the input shaft from application of thethrottle or rotation of the wheel due to the vehicle rolling. When theteeth 212 a and 506 a align to allow engagement as shown in FIG. 8A, theshift cam 320 rotates back to its initial position as shown in FIG. 9Aand the shift fork positioning pin 250 a is pushed up the ramped surfaceof the shift cam 320 towards its final position 304 a. Once the shiftfork positioning pin 250 a is aligned with the first section 304 a ofthe park shift fork groove 304, the biasing force from the shift camspring 322 rotates the shift cam 320 so the shift cam tab 320 a onceagain engages the first wall 303 a of the window 301 c of the shift drumhousing 301 as illustrated in FIG. 9C. When the gearbox 100 is shiftedout of park, motor 400 rotates the shift drum 302. Because the shift camtab 320 a engages the first wall 303 a in the window 301 c of thehousing 301, the shift cam 320 rotates with the shift drum 302 withoutuse of the shift cam spring 322 (direct-couple out). This moves theshift fork positioning pin 250 a of the shift fork 250 out of the firstsection 304 a of the park shift fork groove 304 and into the thirdsection 304 c of the park shift groove which in turn moves the parkshift dog 212 to move the gearing of the gearbox 100 out of park. Asdiscussed above, this feature is called the “direct-couple out” becauseit does not require the use of the shift cam spring. In embodiments, theangular width of the window 301 c is as large or larger that the angulartravel needed to move the shift fork positioning pin 250 a from blockedposition illustrated in FIG. 9A to the in gear positioned illustrated inFIG. 9C.

FIGS. 10 and 11 illustrate another embodiment of a shift assembly thatimplements a flat disk cam instead of a shift drum as described above.The shift assembly (shift cam disk cam assembly 900) of FIGS. 10 and 11includes a shift cam disk 908. The shift cam disk 908 includes shiftcutout passage guides 907 a and 907 b which act as the shift forkgrooves 304 and 308 of the shift drum 302 of the shift drum assembly 300discussed above. For example, a shift fork pin 930 a of a shift fork 930is received in the shift cutout passage 907 a. A pin (not shown) of apark shift fork 932 would be received in shift cutout passage 907 b. Theshift fork 930 is slideably mounted on a second shift shaft 942 similarto shift shaft 242 discussed above. A shift fork biasing member 933mounted on the second shift shaft 942 biases the shift fork 930. Theshift fork 930 engages a shift dog 913 that is slideably mounted on aninput shaft 912 in this embodiment. Also illustrated as being mounted onthe input shaft 912 in this embodiment are bearings 971 and 972, gear915 and sprocket 971.

Sprocket 971 is rotational coupled to sprocket 960 via chain 961.Sprocket 960 is mounted on a second shaft 970. Also mounted on thesecond shaft 970 are bearings 962 and 950 that would be received inrespective housing seats (not shown). Further gears 952, 954, 956 and apark lock gear 958 are also mounted on the second shaft 970. The parklock gear 958 includes holding slots 958 b that are positioned betweenpark gear teeth 958 a. The disk cam assembly 900 also includes a parkpawl 920. The park pawl 920 has a first end 920 a that is designed tofit in the holding slots 958 b of the park lock gear 958 to lock thegearbox 100 in park. The park pawl 920 further has a mid portion 920 bthat is rotationally mounted on a park pawl shaft 942. A pawl biasingmember 924 mounted on the park pawl shaft 922 biases the park pawl 920so the first end 920 a of the park pawl 920 is biased out of the holdingslots 958 b of the park lock gear 958. Moreover, the park shift fork 932is configured and arranged to the selectively align the park lock gear958 with the park pawl 920. A parking ramp 911 extends from a surface ofthe shifting cam disk 908. A second end 920 c of the park pawl 920selectively engages the parking ramp 911 of the shifting cam disk 908when the shifting cam disk 908 is rotated. The parking ramp 911 assertsa force on the second end 920 c of the park pawl 920 to counter thebiasing force of pawl biasing member 924. As a result, the first end 920a of the park pawl 920 is received in a holding slot 958 b of the parklock gear 958 which locks the transmission in park. The transmissionwill remain locked in park until the shifting cam disk 908 is rotated.The parking ramp 911 feature could be separate part that is connected tothe shifting cam disk 908 via spring to provide a similar function asthe cylindrical shift drum assembly described above.

The shifting cam disk 908 is rotated by a shifting cam disk shift shaft904. A shift gear member 905 that is locked in rotation with theshifting cam disk shift shaft 904 includes shift gear teeth 905 b whichmate with shifting cam disk teeth 903 on a centrally located positionshaft 909 of the shifting cam disk 908. Coupled to the position shaft909 is a position sensor 912 configured to sense the then current gearposition of the gearbox 100. This embodiment further illustrates a bellcrank 902 that is mounted to the shifting cam disk shift shaft 904 viafastener 911 and a detent plunger assembly 906. Rotation of the bellcrank 902 changes gearing. The detent plunger assembly 906 isoperationally coupled to the position shaft 909 to adjust a gear settingof the shifting assembly 900 if needed. As discussed above, the rampfeature 911 coupled to the shifting disk 908, in an embodiment, providessimilar functionality as the shift cam 320 arrangement in shifting intoand out of gears of the gear box 100.

Referring to FIG. 12, a block diagram of a shift control system 600 ofone embodiment is illustrated. As illustrated, the shift control system600 includes a controller 602 that is coupled to receive signals from aposition sensor 606. The controller 602 (engine control unit in anembodiment) utilizes a detent control algorithm stored in its memory 604to control the motor 400. In embodiments, after the system receivesshift command from the operator, the motor 400 is energized undercontrol of the controller 602 to drive the shift drum 302 to a specificangular target position where it is to remain until a subsequent shiftoccurs by the operator. Also illustrated in the block diagram are inputs610 (1-n). An operator of the vehicle uses the inputs 610 (1-n) toconvey signals to the controller 602 to shift gears. The electric shiftconfiguration of embodiments makes it possible to have multiple inputs610 (1-n). For example, there can be independent inputs (switches,levers, dials, buttons, etc.) to select different gear ranges and orfunctions. In particular, embodiments allow for different operator shiftschemes that are optimized for a vehicle's particular market. Forexample, this will allow the “direction function” and the “gear rangefunction” to be split between multiple operator devices. A first input610-1 could be used to select between high, low and park ranges and asecond input 610-2 could be used to select between forward and reverse.Moreover, the inputs 610 (1-n) can include vehicle inputs such as, butnot limited to, ground speed, engine speed, throttle position, etc. thatthe controller 602 uses to determine when to shift gears.

The controller 602 may be implemented in digital electronic circuitry,or with a programmable processor (for example, a special-purposeprocessor or a general-purpose processer such as a computer) firmware,software, or in combinations of them. Apparatus embodying thesetechniques may include appropriate input and output devices, aprogrammable processor, and a storage medium 604 tangibly embodyingprogram instructions for execution by the programmable processor. Aprocess embodying these techniques may be performed by a programmableprocessor executing a program of instructions to perform desiredfunctions by operating on input data and generating appropriate output.The techniques may advantageously be implemented in one or more programsthat are executable on a programmable system including at least oneprogrammable processor coupled to receive data and instructions from,and to transmit data and instructions to, a data storage system, atleast one input device, and at least one output device. Generally, aprocessor will receive instructions and data from a read-only memoryand/or a random access memory. Storage devices suitable for tangiblyembodying computer program instructions and data include all forms ofnon-volatile memory, including by way of example, semiconductor memorydevices, such as EPROM, EEPROM, and flash memory devices; magnetic diskssuch as internal hard disks and removable disks; magneto-optical disks;and CD-ROM disks. Any of the foregoing may be supplemented by, orincorporated in, specially-designed application-specific integratedcircuits (ASICs).

As discussed above, embodiments use a control algorithm to determinewhen to shut the motor 400 off as it reaches a target position of aselect gear. Due to mechanical inertia and reaction time of theelectronic controller 602, there is some tolerance in the stop position.Hence, an acceptable tolerance window is applied. Even with a fairlywide window for a target, however, there is a possibility that the motorwill stop at the edge of the target window. The slightest mechanicalmovement of the drum 302 or electrical signal drift\noise could resultin the system being seen as out of the target window. This would causethe motor 400 to energize briefly to jog the drum 302 a very smallamount. The motor 400 could end up dithering (turn on, off, on, off,etc.) if it ends up sitting right at the boundary of the targetposition. The issue is how to hold the mechanical components in aposition while the vehicle is subject to vibration. Although amechanical, spring-loaded, detent system could be used it would addcomponents and cost to the overall system. To help minimize motor sizeand cost the current draw in duty cycle of the motor needs to beminimized during shifting events. “Dithering” can result in undesirableload cycles, noise, heat, and current draw on the vehicles electricalsystem. As discussed above, embodiments of the present invention use anelectronic detent control algorithm to address this problem. Inparticular, embodiments use the electric motor 400 and the positioncontrol algorithm to prevent unwanted dithering and to act as anelectronic detent.

Referring to FIG. 13A a target window pie chart 620 of an embodiment isillustrated. The pie chart 620 represents the angular position and sizeof an “in-gear” section of cam tracks 304, 308. The target windowincludes a fine adjustment window 624 that is a narrow window that iscentered on the nominal target. The target window further includes acourse adjustment window 622 that is a wider window that is alsocentered on the nominal target. The span between the fine adjustmentwindow 624 and the course adjustment window 622 is sufficiently large sothat small mechanical movement of the shift assembly (such as the shiftdrum assembly 300 or shift cam disk assembly 900 discussed above) orsmall electrical signal variations will lie between these two limits.The total width of the course adjustment window 622 is narrower thanshift drums “in-gear” width of the cam track “flat” (i.e. is within anacceptable range for its select gear). In embodiments, as the motor 400drives the shift assembly to a target position, the position sensor 606will first see the setting of the shift assembly pass by the edge of thecourse adjustment window 622, then eventually see the setting of theshift assembly enter the fine adjustment window 624. Once the fineadjustment window 624 has been reached, the controller 602 implementingthe control algorithm commands the motor 400 to turn off. The controlalgorithm will not tell the motor 400 to turn on to correct a shiftassembly setting (due to mechanical movement or electric signal noise,until the deviation from the target is sufficiently large to falloutside the course adjustment window 622. This prevents the controller602 from constantly cycling the motor on and off (dithering) in order todeal with small mechanical movements of the shift assembly or smallelectrical noise in the control signals. FIG. 13B illustrates a drum camtrack graph 630 which traces out a centerline of the shift drum camtracks 304 and 308 of the shift drum 302 of the shift drum assembly 300in an unwrapped flat pattern. The angular span of the course adjustmentwindow 622 is less than the width of the in-gear portion 636 (range) ofthe cam track 308. Each “flat” section of the cam tracks 304 and 308 iswhere the fork/dog clutch 250, 256, 212, 226 is held in a particulargear.

FIG. 14 illustrates an operation flow diagram 700 of one embodiment. Theprocess starts with the operator selecting a new gear position (702).Once a new gear position has been selected the engine control unit 602looks at a drum position signal from the drum position sensor 606 anddetermines the direction the motor needs to run to get to the desirednew gear position (704). The motor 400 rotates the shift assembly in thedesired direction. The position sensor 606 provides angular positionfeedback (706). Receiving signals from the position sensor 606, theengine control unit 602 monitors the setting of the shift assemblypassing through the course adjustment window 624 boundary towards thenominal target (607). Once the engine control unit 602 observes thesetting of the shift assembly passing through the fine adjustment window624 boundary, the engine control unit 602 stops the motor 400 (714).Subsequently, if the shift assembly setting (such as the position of theshift drum 302) unintentionally rotates a small amount due to vibration,or the engine control unit 602 sees slight variation in the electricalsignal, causing the engine control unit 602 to see that it has movedoutside the fine window adjustment window 624 but still within thecourse adjustment window 622, the engine control unit 602 keeps themotor off (714). If the shift drum 302 unintentionally rotates enough tomove past the boundary of the course adjustment window 622, the enginecontrol unit 602 commands the motor 400 to rotate the shift drum 302back towards the nominal target position (714). Once a drum has againreached the fine adjustment window 624, the motor 400 shuts off (716).The system then continues to monitor the shift drum's position at (712)(i.e. the setting of the shift assembly).

FIGS. 15A through 15E illustrate a target window pie chart 800 with anominal target position 802 and how the detent control algorithm worksin an embodiment. FIG. 15A illustrates the target window pie chart 800as a new command to shift to a new target position is provided. Themotor 400 turns on to rotate the shift drum 302 so the nominal targetposition 802 setting of the shift assembly is within the target windows.FIG. 15B illustrates that the nominal target position 802 is now withinthe course window 804 but has not yet reached the fine window 806 so themotor 400 continues to drive. FIG. 15C illustrates that the nominaltarget position 802 has now reached the fine window 806 so the motor 400is turned off. FIG. 15D illustrates the situation where the shift drum302 is rotated due to vibration, but is still within the course window804. In this situation the motor 400 stays off. FIG. 15E illustrateswhere the shift drum 302 has rotated enough to fall outside the coursewindow 804. In this situation, the motor 400 would be turned on by thecontroller 602 to jog the position of the shift drum 302 back into thefine window 806.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiment shown. This applicationis intended to cover any adaptations or variations of the presentinvention. For example, transmission and gearing system for some drivelines may not need “park gear” of the manual override. Therefore, it ismanifestly intended that this invention be limited only by the claimsand the equivalents thereof.

1-22. (canceled)
 23. A shift drum assembly for a gear box of atransmission, the shift drum assembly including: a shift drum housinghaving at least one groove guide with a select profile that isconfigured to receive at least one shift fork positioning pin of a shiftfork, the shift drum housing further having a window; a shift camrotationally coupled to the shift drum, the shift cam having a shift camtab positioned within the window of the shift drum; and a bias memberconfigured to bias the shift cam in relation to the shift drum to createa preload force used at least in part to complete a shift when a blockedshift condition of the gear box is encountered.
 24. The shift drumassembly of claim 23, further comprising: the shift drum having a shiftdrum post, the shift cam received around the shift drum post.
 25. Theshift drum assembly of claim 24, further comprising: the bias memberreceived around the shift drum post; the shift drum post having a springholding aperture; the shift cam having a spring holding slot; and afirst end of the bias member received with the spring holding slot ofthe shift cam and a second end of the bias member received within thespring holding aperture of the shift drum post.
 26. The shift drumassembly of claim 23, further comprising: the at least one groove guideformed by at least one portion of the shift cam; the at least oneportion of the groove guide formed by the shift cam having a rampsection; the a window of the shift drum housing having a first side walland a second side wall; the shift cam tab of the shift cam configured tobe initially biased against the first side wall of the window of theshift drum housing during the blocked shift condition, wherein rotationof the shift drum housing in a first direction counters a bias force ofthe bias member via the at least one shift fork positioning pin of theshift fork engaging the ramp section of the at least one groove guide ofthe shift cam allowing the shift cam tab of the shift cam to movetowards the second side wall of the window of the shift drum thereincreating additional torsion preload while allowing the shift drumhousing to reach a target angular position even though the shift cam andthe shift fork positioning pin have not moved thereby creating a stateof preload.
 27. The shift drum assembly of claim 26, further whereinmovement of the shift fork positioning pin up the ramp section of theshift cam is configured to cause the shift drum assembly to complete theshift.
 28. The shift drum assembly of claim 27, wherein movement of theshift fork positioning pin up the ramp section of the shift cam iscaused by at least one of rotation of a wheel operationally coupled tothe at least one shift fork positioning pin and rotation of an inputshaft to the gear box that is operationally coupled to the at least oneshift fork positioning pin.
 29. The shift drum assembly of claim 23,wherein the shift cam tab of the shift cam is configured to engage thefirst side wall of the window of the shift drum housing during rotationof the shift drum housing in a second direction.
 30. A transmissioncomprising: a plurality of gearing assemblies operationally coupledtogether to provide a select rotational output from a rotational inputof an input shaft to the transmission; at least one shift forkconfigured and arranged to change gearing of the gearing assembly; ashift drum housing forming at least a portion of at least one grooveguide, the at least one groove guide having a select profile thatincludes a ramp section, the at least one groove guide configured andarranged to receive at least one shift fork positioning pin of the atleast one shift fork, the shift drum housing further having a window; ashift cam rotationally coupled to the shift drum, the shift cam having ashift cam tab positioned within the window of the shift drum; and a biasmember configured to bias the shift cam in relation to the shift drum tocreate a preload force used at least in part to complete a shift when ablocked shift condition of a gear box of the transmission isencountered.
 31. The transmission of claim 30, further comprising: theshift drum having a shift drum post, the shift cam received around theshift drum post.
 32. The transmission of claim 30, further comprising:the bias member received around the shift drum post; the shift drum posthaving a spring holding aperture; the shift cam having a spring holdingslot; and a first end of the bias member received with the springholding slot of the shift cam and a second end of the bias memberreceived within the spring holding aperture of the shift drum post. 33.The transmission of claim 30, further comprising: the at least onegroove guide formed by at least one portion of the shift cam; the shiftcam including the ramp section of the at least one groove guide; the awindow of the shift drum housing having a first side wall and a secondside wall; the shift cam tab of the shift cam configured to be initiallybiased against the first side wall of the window of the shift drumhousing during the blocked shift condition, wherein rotation of theshift drum housing in a first direction counters a bias force of thebias member via the at least one shift fork positioning pin of the shiftfork engaging the ramp section of the at least one groove guide of theshift cam allowing the shift cam tab of the shift cam to move towardsthe second side wall of the window of the shift drum therein creatingadditional torsion preload while allowing the shift drum housing toreach a target angular position even though the shift cam and the shiftfork positioning pin have not moved thereby creating a state of preload.34. The transmission of claim 33, further wherein movement of the shiftfork positioning pin up the ramp section of the shift cam is configuredto cause the transmission to complete the shift.
 35. The transmission ofclaim 33, wherein movement of the shift fork positioning pin up the rampsection of the shift cam is caused by at least one of rotation of awheel operationally coupled to the at least one shift fork positioningpin and rotation of the input shaft to the transmission that isoperationally coupled to the at least one shift fork positioning pin.36. The transmission of claim 30, wherein the shift cam tab of the shiftcam is configured to engage the first side wall of the window of theshift drum housing during rotation of the shift drum housing during ashift.
 37. The transmission of claim 30, wherein the shift cam tab ofthe shift cam remains engaged with the first side wall of the windowwhen the shift drum housing rotates in a second direction.
 38. Atransmission system for a vehicle implementing a gearbox with shiftdogs, the transmission system comprising: an input shaft: a plurality ofgearing assemblies operationally coupled together to provide a selectrotational output from a rotational input of the input shaft: at leastone shift fork configured and arranged change gearing of the gearingassembly; a shift drum housing having a window; a shift cam rotationallycoupled to the shift drum and forming with the shift drum at least onegroove guide with a select profile that is configured to receive atleast one shift fork positioning pin of the at least one shift fork, theshift cam having a shift cam tab positioned within the window of theshift drum; and a bias member configured to bias the shift cam inrelation to the shift drum to create a preload force used at least inpart to complete a shift when a blocked shift condition of the gear boxis encountered.
 39. The transmission system of claim 38, furthercomprising: the shift drum having a shift drum post, the shift camreceived around the shift drum post.
 40. The transmission system ofclaim 38, further comprising: the bias member received around the shiftdrum post; the shift drum post having a spring holding aperture; theshift cam having a spring holding slot; and a first end of the biasmember received with the spring holding slot of the shift cam and asecond end of the bias member received within the spring holdingaperture of the shift drum post.
 41. The transmission system of claim38, further comprising: the at least one groove guide formed by at leastone portion of the shift cam; the at least one portion of the grooveguide formed by the shift cam having a ramp section; the a window of theshift drum housing having a first side wall and a second side wall; theshift cam tab of the shift cam configured to be initially biased againstthe first side wall of the window of the shift drum housing during theblocked shift condition, wherein rotation of the shift drum housing in afirst direction counters a bias force of the bias member via the atleast one shift fork positioning pin of the shift fork engaging the rampsection of the at least one groove guide of the shift cam allowing theshift cam tab of the shift cam to move towards the second side wall ofthe window of the shift drum therein creating additional torsion preloadwhile allowing the shift drum housing to reach a target angular positioneven though the shift cam and the shift fork positioning pin have notmoved thereby creating a state of preload.
 42. The transmission systemof claim 38, further comprising: a primary clutch that is configured tobe coupled to a motor; a secondary clutch that is configured to be inrotational communication with the primary clutch via belt, the inputshaft operationally coupled to the secondary clutch.